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United States Patent O 3,258,527 INDEX SIGNAL GENERATION Roger D. Thompson, Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Filed Sept.I 24, 1962, Ser. No. 225,525 5 Claims. (Cl. 178-5.4)

This invention relates to index signal-generating apparatus such as used in color television image-reproducing systems and particularly to those ysystems using cathode ray image-reproducing tubes having screens including different color-producing phosphor strips and strip-like formations of index elements from which to derive information regarding the position of an electron beam relative to the color phosphor `strips and in which such information is used to control the electron beam excitation of the screen strips in accordance with color representative signals.

It has been proposed to effect color image reproduction by a cathode ray tube in which the color light-producing phosphors are arranged substantially vertically so that the strips may be exicted in rapid succession by an electron beam traversal of the strips in a series of vertically spaced substantially parallel lines. Such screens are additionally provided with a single set of index strips aligned with (i.e., parallel to) the color light producing phosphor strips so that, when excited by the electron beam, index signals distinctive from the produced light are derived and which are generally indicative of successive positions of the beam as it is deflected over the screen. Such index strips are arranged in predetermined relation to the color phosphor strips. One of the Ways in which such index signals have been used is to control the modulation of the electron beam so that its intensity at any given instant corresponds with the color which it is desired to produce at the same instant that the beam excites a phosphor strip capable of making that color.

The index signals modulated by color representative signals also have been used to vary the rate of the hori- Zontal deflection of the beam over the phosphor strips so that it is retarded in its traverse of those strips capable of making the particular colors represented by the color signals.

Proper excitation of the screen of such an image-reproducing device also has been effected by using the index signals to compensate for such things as non-linearity of beam deflection and unequal width and/ or spacing of the color phosphor strips. Such compensation has been accomplished by varying the beam deflection in accordance with detected deviations of the index signals from a reference.

One of the advantages of controlling either electron beam intensity modulation or beam deflection rate by such index signals is that it is unnecessary to effect particular compensation for any non-linearity of the horizontal beam deflection, non-uniformity in the spacing and/ or Width of the color phosphor strips, and the like. It has been found that such systems work satisfactorily when the index signals are derived from index strips coinciding in position With the color phosphor strips capable of making the particular color corresponding t-o the signal by which the beam is controlled. Also, either one of such systems Works satisfactorily when reproducing desaturated or pastel shades of colors other than that produced by the color phosphor strips with which the index strips are registered. Considerable color distortion is encountered, however, when it is attempted to make highly saturated colors other than that produced by the color phosphor strips with which the index strips are in register. In such cases, the color control Wave derived from the index signals is shifted in phase relative to some reference such as the index strips. When such a phaseshifted color control Wave is used to control the electron beam, either by intensity modulation or by deflection rate variation or by both, a shift in the hue of the color produced by the cathode ray tube is effected, thereby causing a color distortion.

It has previously been proposed to suitably combine the intensity modulation of an electron beam and the beam deflection rate variation to produce highly saturated colors with less color distortion than would be produced by either intensity modulation or deflection rate variation alone. While such a combination effects a substantial improvement in the reproduction of highly saturated colors, there is a practical limit to the saturation which can be achieved without encountering objectionable color distortion.

It is an object of the present invention, therefore, to provide a novel indexing wave-generating system in which the indexing Wave has little or substantially no phase shift relative to a reference.

Another object of the invention is to provide a novel means by which to increase color saturation and at the same time `to reduce color distortion in a color television system employing an image-reproducing device, such as a cathode ray tube, having vertically oriented color phosphor strips.

In accordance with this invention an index signal-generating device is provided with a plurality of sets of index elements arranged in strip-like formations transverse to a specified path. The device also includes means to excite the index elements sequentially along the specified path to produce a plurality of mutually distinguishable sets of index signals by respective ones of the index element sets. The dilferent sets of index signals are separately derived from the device and are combined in such a manner as to produce an indexing wave which has little or substantially no phase shift relative to a reference such as the strip-like formations of index elements.

A typical embodiment of the invention is in an imagereproducing system employing an image-reproducing device, such as a cathode ray tube. The device has a screen comprising a plurality of groups of vertically oriented color phosphor light-producing strips, the individual strips of each group being capable of emitting light of different colors when excited by an electron beam and a plurality of sets of index strips, each set having its own individual response to beam excitation and each response being sufficiently different from the other that a plurality of sets of index signals are developed. These index signals have different phases `by reason of their respective placements on the cathode ray tube screen .and they are combined in such a Way as to produce ya single indexing wave. Such an indexing wave has little or no phase shift, irrespective of the reproduced hue or its saturation. The indexing wave is used to control the excitation of the screen of the image-reproducing device in accordance with the colors to be reproduced. As an illustrative example, the indexing Wave is modulated in phase and amplitude by color representative signals to produce a color control Wave which is used to vary the electron beam intensity or the rate of horizontal 'beam reflection or both.

The invention may be more fully understood from the following description given in connection with the -accompanying drawings, of which:

FIGURE l is a block diagram of a television receiver embodying the invention;

FIGURE 2 is a fragmentary illustration, to an enlarged scale, of a portion of the screen of a color image-reproducing cathode ray tube used in the system of FIGURE l;

FIGURE 3 is a fragmentary illustration, to an enlarged scale, of `another form of screen of a color image-reproducing cathode ray tube which may be used in the system of FIGURE 1 FIGURE 4 is a fragmentary illustration, to an enlarged scale, of still another form of cathode ray tube screen usable in the system of FIGURE 1 and in which the pitch of the index strips differs from the pitch of the respective color phosphor strips;

FIGURE 5 is a series of waveforms shown in relation to the color phosphor and index strips of a cathode ray tube similar to that shown in FIGURE 2 such as would exist when the electron Ibeam is controlled in a manner to produce different highly saturated colors; and

FIGURES 6, 7 and 8 are vector diagrams showing the way in which an indexing wave is produced from the different sets of index signals derived from the screen as shown in FIGURE 2 when different typical highly saturated colors are produced.

A color television receiver embodying7 the invention is generally illustrated in FIGURE 1. The radiated carrier wave, which is modulated by a composite color television signal including a luminance signal component and a chrominance signal component is received by an antenna 10 and processed by any known television receiver 11. Such a composite television signal derived from the receiver 11 is separated by any known means into its various components for operation of a lcolor image-reproducing device such as a cathode ray tube or kinescope 12. This tube is provided with a luminescent screen 13 composed of a multiplicity of groups of vertically oriented phosphor strips, the respective strips of each group being capable of emitting light of different colors when excited by an electron beam. The screen also has a plurality of sets of index strips capable of producing a plurality of mutually distinguishable index signals when excited by a beam. Illustrative details of typical screens in accordance with the invention will ybe described subsequently in connection with FIGURES 2, 3 .and 4. The kinescope also is provided with a beam intensity-controlling electron gun including a cathode electrode 14 `and a grid electrode 15.

The electron beam is deflected both horizontally and vertically to scan the usual rectangular raster of vertically spaced substantially parallel lines transverse to the strips of the screen 13 by means of a first or main deflection yoke 16. The composite color television signal derived from the receiver 11 includes deflection synchronizing pulses which are applied to deflection circuits 17 for energizing the deflection yoke 16 in the usual manner. A second or auxiliary horizontal deflection coil 18 varies the rate of horizontal beam deflection when suitably energized in a manner and for a purpose to be described more fully subsequently. Preferably such a coil is mounted internally of the main deflection yoke 16.

The luminance signal component of the composite signal derived from the receiver 11 is applied to and processed in a luminance signal channel including a luminance signal amplifier 19. As shown in this particular receiver for illustration of the present invention, the luminance signal derived from the amplifier 19 is applied to the grid of the color kinescope 12. The chrominance signal component of the composite signal derived from the receiver 11 is applied to a chrominance signal channel which also includes conventional apparatus for deriving color representative signals from the chrominance component. In the present U.S. standard color television signal the chrominance signal component is a phase and amplitude modulated subcarrier wave having a nominal frequency corresponding to one of the higher video signal frequencies. In the present case this frequency is approximately 3.58 mc. per second.

As is typical in known receivers for such a composite television signal, the chrominance signal component is separated `from the rest of the signal by means such as a chrominance signal bandpass amplifier 20. This amplifier, for example, passes signals in the range from 2 to 4 mc. per second. Thus, the phase and amplitude modulated subcarrier wave is impressed upon one inputcircuit of a color signal demodulator 21. This demodulator is of the synchronous type and is supplied with selected phases of a reference signal wave which has the nominal frequency of the color subcarrier wave. The phases of this wave which are supplied to the color demodulator 21 depend on the particular phase angles at which it is desired to demodulate the color subcarrier wave. As is known in the art such demodulating phases are, to a considerable degree, matters of choice and depend upon such considerations as maximum bandwidth of the signals to be produced, the possible use of matrixing circuits and, if such are used, the character and relative complexity of such circuits, and the like. Accordingly, it will be understood that, for the purpose of describing the present invention, there may be derived from the color demodulator 21 suitable color representative signals. Particularly, such signals usually are termed color difference signals or color minus luminosity signals.

The received composite color television signal also i11- cludes periodic bursts of several cycles of the color subcarrier nominal frequency for use in controlling the phase of the reference signal wave produced by the source 22. Accordingly, the composite color television signal also is impressed upon a burst separator 23 which operates to produce in its output only the periodic color synchronizing signal. Such bursts are impressed upon one of two input circuits of a phase detector 24, the other input circuit having impressed thereon the reference signal wave derived from the source 22. Any phase deviation between these signals is detected and produces in the output circuit of the phase detector a signal indicative of such phase deviation. Such a signal is applied to a phase control device 25 the output of which is connected to the reference signal source 22. In a typical instance where the source 22 is an oscillator, the phase control device 25 may be a reactance tube forming one of the frequency-determining elements of the oscillator. Such arrangements are known and frequently used in systems of this character and hence no further description thereof is necessary.

All of the signal-processing circuits of FIGURE 1 described up to this point may be of the type disclosed in Color Television Service Data-1960, No. TS-for CTClO Chassis Series, furnished by RCA Service Company, Camden, New Jersey, and printed May 10, 1960.

The index signals used in the illustrative embodiments of the invention disclosed herein are in the form of two mutually distinguishable radiations from the screen 13 of the color kinescope 12. Preferably, these radiations are not readily visible to the human eye. Two different sets of index signals thus are derived from the kinescope. The two sets of index signals have different phases by reason of the placement of the index strips on the screen 13 (as more fully described subsequently). The first set of index signals is sensed by a phototube multiplier 26 which either is sensitive only to the particular radiation comprising the first set of index signals or is provided with a filter 27 which passes only this particular radiation. The second set of index signals is sensed by a phototube multiplier 28 which either is sensitive only to radiation comprising the second set of index signals or is provided with a suitable filter 29. Thus, the two differently phased sets of index signals are derived respectively from the phototube multipliers 26 and 28.

In some illustrative embodiments of this invention to be described, the index strips are so placed on the screen 13 of the color kinescope 12 that the two sets of index signals are displaced from one another by One of the sets of derived index signals is reversed in phase relative to the other, as for example, by passing the output of the phototube multiplier 28 through a polarity inverter 31. The two sets of index signals then are impressed upon an index signal adder 32 for combination. An indexing wave is made from the two sets of index signals derived from the index signal adder 32 by passing the signals through such apparatus as an index bandpass filter 33. It is to be understood that the respective indexing w-ave components derived from the two sets of index signals have precisely the same phase only in certain circumstances when particular colors are being reproduced. In other cases, there are departures by the two indexing wave components from identical phase relationship. Such different phases are mutually compensating in accordance with this invention and will be described in more detail later. The composite indexing wave derived from the lter 33 is passed through a delay circuit 34 such as disclosed in Patent 2,967,210, issued January 3, 1961, to R. D. Kell. Such a delay circuit compensates for inherent delays of the indexing wave so that the Wave derived by beam deection in one horizontal raster line is used for beam control during the next succeeding (in time) raster line.

The indexing wave is impressed upon an index signal modulator 35 which also receives the color representative signals derived from the color signal dernodulator 21. The index signal modulator 35 may be any known device (such yas that used in the TX-lB Colorplexer manufactured by Radio Corporation of America) by which to produce a color control wave which is phase and amplitude modulated by color representative signals.

The output of the index signal modulator 35 is coupled to a color signal amplier 36. The output of this ampliiier is impressed upon the cathode 14 of the color kinescope 12 for control of the intensity of the electron beam in combination with that effected by the control grid 15 in response to the luminance signal component of the cornposite color television signal. The output of this amplier also is impressed upon the auxiliary deection coil 18 which modifies the beam deflection produced by the main deflection yoke 16 so that the beam is retarded as it traverses the color strips capable of producing the color represented by the color signals and is accelerated as it traverses other color strips. Each point of beam retardation is determined by the hue of the image area as represented by the phase of the color control wave applied to the coil 18. The amount of beam retardation is determined by the amplitude of the color control wave applied to the coil 18.

It is to be understood that the practice of the present invention is not limited to any particular way in which the screen of the color kinescope is excited. Such excitation may be effected by electron beam intensity or beam deflection Variation individually or by a combination of these two devices as disclosed in FIGURE l. Alternatively, the color control wave may be used only to compensate for non-linearity of horizontal beam deflection, unequal width and/ or spacing of the color strips and the like as disclosed in Patent 2,921,117, issued January 12, 1960, to Arthur Liebscher.

Before describing the manner in which unwanted phase deviations of a single indexing signal wave are caused and the compensation of them provided by the plurality of sets of index signals in accordance with the instant invention, reference next will be made to FIGURE 2 for .a more detailed description of Ia representative screen 13 of the color kinescope 12 of FIGURE 1. As previously indicated, the screen is composed of a multiplicity of groups of three different color light-producing phosphor strips such as the red, blue and green strips 37, 38 and 39 respectively. In the present example, the red strips 37 are substantially twice as wide as each of the blue and green strips 38 and 39. A second group of color phosphor strips 37', 38' and 39 is shown following the rst group in the indicated direction of scanning. A first group of index strips Il having substantially the same width as each of the blue and green strips is interleaved between the red and blue strips. A second set of index strips I2, also having the same width as each of the blue and green strips is interleaved between the green and red strips. The particular materials of which the index strips I1 and I2 are made preferably are such that they produce radiations, when excited by an electron beam, which are invisible and are separable preferably, but not necessarily, by optical means. For example, the I1 and I2 strips may have respective peak radiations at about 3400 and 3800 Angstrom units, both of which are in the ultraviolet range of the spectrum. By reason of the described widths of the color and index strips, an index signal is derived from each of the index strips I1 and I2 during each color cycle. The index strips I1 .and I2 are equally spaced with respect to one another. As a result, the index signals derived from the strips I1 are 180 electrical degrees displaced with respect to the index signals derived from the strips I2. As is common practice in cathode ray tubes of this type, the screen 13 may be covered on the side toward the electron gun by a metallic backing 41 such as a layer of aluminum which is sufciently thin to be pervious to the electron beam.

Reference now is made to FIGURE 3 for a description lof an alternative form of the color kinescope screen 13. In this case the red, blue and green strips 42, 43 and 44 respectively have equal widths. This screen lalso may be provided with a metallic backing 41. In this form of screen, the rst set `of index strips I1 is located on the electron gun side of the metallic layer 41 and each is approximately half the Width of the color phosphor strips. The strips I1 are located substantially in register with the left hand portions of the blue color phosphor strips 43 as viewed from the front of the tube and in the drawing.

A second set of index strips I2 is placed on the back of the metallic layer 41 substantially in register with the right hand portions of the green color phosphor strips 44. By reason of such a strip placement, a first set of index signals derived from the strips I1 is developed for each color group. Also, a second set of index signals derived from the strips I2 is developed for each color group. In addition, the index signals derived from the strips I1 bear a 180 phase relation to the index signals derived from the strips I2 as in the form of the screen shown in FIGURE 2. It will be understood that other screen congurations may be used in embodiments of this invention to produce two or more sets of index signals having substantially any desired repetition rate and phase relationship to one another.

FIGURE 4 shows a screen configuration in which only one index strip in each of two sets is used for every two groups of color strips. The screen 13 has color strips such as the red, blue and green strips 42, 43 and 44 of equal widths as in the arrangement of FIGURE 3. Index strips I1 are placed centr-ally in back of every other one of the red color strips such as the strips 42 and 42.". Index strips I2 are placed in back of every other junction between the blue and green color strips such as the strips 43-44 and 43"-44. No indexing strips are associated with the intervening color strips 42', 43' and 44. It is seen that the `two sets of index strips I1 and I2 bear -a 180 phase relationship to one another in terms of the repetition rate of the groups of color strips.

As a result of such an arrangement only half the number of indexing signals are produced .as compared with the arrangements of FIGURES Zand 3 so that any composite indexing wave produced from such signals wouldl have only half the desired frequency for modulation by the color signals. When using such an arrangement as that shown in FIGURE 4, therefore, it is merely necessary to double the frequency of the two derived sets of index signals or of the component indexing waves derived therefrom in order to produce an indexing wave having the desired frequency.

Reference now will be made to FIGURE 5 for an explanation of the manner in which -an indexing wave derived from only one set of index strips is undesirably shifted in phase when the intensity of the electron beam is modulated to produce highly saturated colors and the manner in which such phase shift is obviated by the present invention. For purposes of this explanation, the

screen structure in accordance with FIGURE 2 will be considered. A fragmentary portion of such a screen is reproduced in this gure and used as a reference for the various waveforms also shown representing the operation of the apparatus embodying this invention. The spacings between centers of the screen strips have been indicated in degrees of a complete color cycle for reference purposes. The ensuing description deals with three typical phase relationships of the color control Wave to the index strip sets, viz: (1) 0 and 180 phases respectively as when producing magenta; (2) 90 and 270 phases respectively as when producing red; and (3) phases other than 90 and multiples thereof as when producing blue or green.

A typical and 180 phase relationship between control wave and index strips is Considered first. The sinusoidal wave 45 shown partly in broken and partly in full lines, is a representation of the screen excitation by the electron beam when it is desired `to make a highly saturated magenta portion of the reproduced image. Such an image portion is reproduced by developing substantial amounts of red and blue light and a minimum amount of green light. This wave has a maximum peak occurring when the beam is positioned between the red and blue strips 37 and 38 and coinciding in time with the traversal of the electron beam over the center of the index strips Il. The wave has a minimum peak at a time corresponding to the traversal of the index strips I2. The maximum excitation of the screen 13 is obtained while the beam is traversing the red and blue color strips 37 and 38, thereby producing considerable red and blue light. A minimum of green light is produced because of relatively low screen excitation while the beam is traversing the green color strip 39. The combination of such light emanating from the screen is generally of a highly saturated magenta.

Because the screen excitation is maximum, as represented by the full line curve portion 46, during beam impingement upon the index strip I1, the index signal produced is a symmetrical pulse 47 of substantial amplitude. Because the screen excitation is minimum, as indicated by the solid line curve portion 48, during beam traversal over the index strip I2, the resulting index signal pulse 49 is symmetrical and of relatively small amplitude. Considering the relative dispositions of the index strips I1 and I2 with respect to the red, blue and green color strips 37, 38 and 39, the first set of index signals 47, 47' etc., is retarded in phase from the centers of the red color phosphor strips 37, 37' by substantially 90. From the same consideration of strip arrangement, the second set of index signals 49, 49 is advanced in phase by substantially 90 relative to the centers of the red Color phosphor strips.

These two sets of index signals, which are derived separately from the screen of the color kinescope 12 of FIGURE 1 by means of the photomultipliers 26 and 28 respectively, are combined to form a composite indexing wave as previously described after inverting the polarity of one of the sets of signals. Such combinations of these index signals in accordance with the present invention may best be understood by reference to the vector diagram of FIGURE 6. The Vectors R, B and G represent respectively the excitation of the red, blue and green color strips 37, 38 and 39 of FIGURE 5 to produce a highly saturated magenta color. As previously described, the red and blue light-producing portions of the color control wave have substantial amplitude as represented by the lengths of vectors R and B. Similarly, the green light-producing portion of the color control wave is of relatively small magnitude as represented by the length of the vector G. Also, the indexing wave component produced from the index signals derived from the rst set of index strips I1 is represented by the vector Il which lags vector R by substantially 90 and is of considerable magnitude. In a similar manner the indexing wave component produced by the second set of index signals derived from the index strips I2 is represented by the vector I2 which leads the vector R by substantially 90 and is of small magnitude. This vector diagram also illustrates the inversion of the second set of index signals represented by lthe vector I2 and is shown in FIGURE 6 as vector I2 which is in-phase with the vector Il. The combination of the two sets of index signals, thus, produces the composite indexing wave represented by the vector Il for color signal modulation by the index signal modulator 35 of FIGURE I. This composite indexing wave has a 0 phase relationship to the index strips Il and a 180 phase relationship to the index strips I2.

The operation of the system embodying the present invention next will be described in a typical situation where the color control wave bears a relationship to the index strips, such as when it is desired to reproduce a highly saturated red portion of the image. The color control Wave, by which screen excitation is eifected, is represented by the sinusoidal curve 51 of FIGURE 5. The screen excitation is maximum, as indicated by the maximum peak 52 of the curve S1, coinciding with the beam traversal of the center of the red color strip 37 and is minimum, as indicated by the minimum peak 53 of the curve 51, coinciding with the beam traversal of the boundary between the blue and green color strips 38 and 39 respectively. Thus, a substantial amount of red light and minimum amounts of blue and green light are developed. While the beam is traversing the indexing strip Il the screen excitation has a decreasing intensity, thereby producing an index signal 54 which is unsymmetrical in one sense. The screen excitation increases as the beam traverses the index strip I2 so that an index signal 55 is generated which also is unsymmetrical, but in the opposite sense to the index signal 54.

Because of their unsymmetrical natures, the index signals 54, 54', etc., produce an indexing wave component which is advanced in phase relative to the phase of the desired indexing wave `and the index signals 55, 55', etc., produce an indexing wave component which is retarded in phase relative to the phase of the desired indexing wave. The vector diagram of FIGURE 7 indicates these phase relationships. The respective lengths of the vectors R, B and G indicate substantial excitation of the red color .strips and minimum excitation of the `blue and green color strips, thereby producing a highly saturated red portion of the image. Because the index signals 54, 54', etc., and 55, 55', etc., are unsymmetrical in opposite senses and have corresponding amplitudes, the indexing wave components produced therefrom are indicated by the substantially equal length vectors I1 and I2 which are respectively advanced and retarded in phase relative to the desired indexing Wave represented by the vector I. The combination of these two wave components, after phase inversion of the wave component represented by the vector I2 as indicated by the vector 12, produces a desired composite indexing wave I. This indexing wave bears a substantially 0 phase relationship to the index strips Il and a substantially phase relationship to the index strips I2 as in the previously described example. Thus, there is no appreciable, if any, phase shift of the composite indexing wave effected when either highly saturated red or highly saturated magenta is produced.

An example of the operation of the system embodying the present invention when it is desired to make a highly saturated color by means of a color control wave which bears a phase relationship to the index strips I1 and I2 of the screen 13 which is not 90 or a multiple thereof, also is indicated in FIGURE 5. A color control wave 56 excites the screen -13 to make a highly saturated blue portion of the image. The screen excitation is maximum, as indicated by the peak 57 of the Wave 56, and coincides in time with the beam `traversal over the blue strip 38. The screen excitation is minimum, as indicated by the peak 58 of the Wave 56, and coincides in time with the traversal of the beam over a marginal portion of the red phosphor strip 37. While the beam is traversing the index strips I1 the screen excitation increases, as shown by the curve 56 so as to produce index signals 59, 59, etc., of substantial m-agnitude and which are unsymmetrical in one sense. During the beam traversal of the index strips I2 the screen excitation decreases so as to produce index signals 61, 61', etc., which are of relatively small magnitude and which are unsymmetrical in a sense opposite to the index signals 59, 59', etc.

FIGURE 8 represents vectorially the opera-tion of the system for producing highly saturated blue portions of the image. The vector B represents the phase and amplitude of the color control wave 56 of FIGURE 5 for maximum excitation of the blue color strips and, hence, is of considerable magnitude. The vectors G and B are of relatively small magnitudes representing, respectively the relatively small excitation off the green and red color strips of the screen. The vectors I1 and I2 represent respectively the indexing wave components produced by the index siggals from strips with corresponding designations. Because of the unsymmetrical character of the index signals 59, 59 of FIGURE 5, the vector I1 is retarded in phase relative to the desired indexing wave represented by the vector I and is of substantial magnitude corresponding to the amplitude of the index signals I59, 59. The vector I2 is advanced in phase relative to the desired indexing wave vector I and is of smaller magnitude than the vector I1, corresponding to the lamplitude of the index signals 61, 61. Owing to the smaller amplitude and unsymmetrical shape of the index signals `61, 61 the indexing Wave component produced thereby is advanced in phase more than the indexing wave component produced by the larger amplitude index signals 59, 59' is retarded in phase. The inversion of the second set of index signals to produce an indexing Wave component represented by the vector I2 of FIGURE 8 and its combination with the indexing wave component represented by the vector I1 produces a composite indexing wave represented by the vector I. This indexing Wave bears a substantially phase relationship to the index strips I1 and a substantially 180 phase relationship to the index strips I2 as in the two previously de scribed examples.

The operational example represented by the vector d-iagram of FIGURE 8 illustrates one of the important ifeatures of the present invention. It is a characteristic of the system that the phase shift of the indexing wave component of greater amplitude is less than the phase shift of the indexing wave component of smaller amplitude. Thus, as indicated in this figure, even though the indexing Wave component represented by the vector-I2 is shifted in phase through a greater angle than the indexing wave compo nent represented by the vector I1 `of greater amplitude, the combination of these two wave components is such that 4the resultant composite indexing wave has very little, if any, phase shi-ft.

The composite indexing wave produced from the screen structure of FIGURE 2 operating in accordance with the three examples described has substantially no phase shift regardless of the particular colors reproduced or of the saturation of these colors. It also is evident that there is substantially no amplitude change in the indexing wave effected by the production of any of the image colors of a given saturation. Because of the different peak amplitudes of the indexing Wave to produce colors of varying saturation, there may be some amplitude variation of the composite indexing wave resulting therefrom. This, however, is of no particular importance because, if desired, the system may be provided with suitable facilities such as amplitude limiters to insure that the indexing wave impressed upon the index signal modulator 35 of FIGURE 1 has a substantially constant amplitude. Alternatively, these small amplitude variations may be retained so as to be present in the color control wave derived from the modulator 35. In such case the amplitude of the control wave is automatically decreased when it is desired to reproduce colors the screen strips of which lie between the index strips, whereby greater stability of operation may be achieved.

Analysis of the operation of the system when the color kinescope employs a screen such as shown in FIGURE 3 may be made in a manner similar to that described with reference to FIGURES 5, 6, 7 and 8. Such analysis will show that the system operates substantially in the same manner described for a color kinescope having a screen such as that shown in FIGURE 2.

Likewise, the oper-ation of the system when a screen structure such as that shown in FIGURE 4 is employed in the color kinescope may be similarly analyzed, taking into consideration that the composite indexing wave impressed upon the index signal modulator 35 of FIGURE 1 will have a frequency twice that produced directly from the half-frequency indexing strips of FIGURE 4. In such case, it is seen that the system will operate substantially in a manner identical to that described with reference to a color kinescope having a screen such as either of those shown in FIGURES 2 and 3.

What is claimed is:

1. In a color television image-reproducing system, the combination including:

a cathode ray tube having a screen comprising a plurality of groups of vertically oriented equal width color phosphor strips, the strips of each group being capable of emitting light of different colors when excited by an electron beam, and two sets of index strips aligned with said phosphor strips and capable respectively of producing two mutually distinguishable sets of index signals when excited by an electron beam, there being one of each set of index strips for each group of color phosphor strips and the index strips being of equal Widths corresponding substantially to one-half the width of one of said color phosphor strips and equally spaced from one another;

means for separately deriving said two sets of index signals from said cathode ray tube screen, the two sets of index signals being of opposite polarities;

means for Combining said two sets of index signals to produce an indexing wave having little or no phase shift relative to said index strips;

means for modulating said indexing wave in phase in accordance with hue and in amplitude in accordance with saturation by color representative signals to produce a color control wave; and

means responsive to said color control wave to vary said electron beam excitation of said cathode ray tube screen in accordance with the image colors to be reproduced.

2. In a color television image-reproducing system, the

combination including:

a cathode ray tube having a screen comprising a plurality of groups of vertically oriented color phosphor strips, the strips of each group being capable of emitting light of different colors when excited by an electron beam and one of the color phosphor strips of each group being of lesser width than at least one other color phosphor strips of the group, and two sets of index strips aligned with said phosphor strips and capable respectively of producing two mutually distinguishable sets of index signals when excited by an electron beam, there being one of each set of index strips for each group of color phosphor strips and the index strips being of equal widths corresponding substantially to the width of one of said color phosphor strips and equally spaced from one another;

means for separately deriving said two sets of index signals from said cathode ray tube screen, all of said index signals having the same polarity;

means for combining said two sets of index signals in opposite polarities to produce an indexing wave having little or no phase shift relative to said index strips; .s

means for modulating said indexing wave in phase in accordance with hue and in amplitude in accordance with saturation by color representative signals to produce a color control wave; and

means responsive to said color control wave to vary said electron beam excitation of said cathode ray tube screen in accordance with the image colors to be reproduced.

3. In a color television image-reproducing system, the

combination including:

a cathode ray tube having a screen comprising a plurality of groups of vertically oriented color phosphor strips, the strips of each group being capable of emitting light of different colors when excited by an electron beam and oneV of the color phosphor strips of each group being of greater width than the other color phosphor strips-of the group, and two sets of index strips aligned with said phosphor strips and capable respectively of producing two mutually distinguishable sets of index signals when excited by an electron beam, there being one of each set of indexing strips for each group of color phosphor strips and the indexing strips being of equal widths and equally spaced from one another;

means for separately deriving said two sets of index signals from said cathode ray tube screen;

means for combining said two sets of index signals in opposite phase to produce an indexing wave having little or no phase shift relative to said index strips; i

means for modulating said indexing wave in phase in accordance with hue and in amplitude in accordance with saturation by color representative signals to produce a color control wave; and

means responsive to said color control wave to vary said electron beam excitation of said cathode ray tube screen in accordance with the image colors to be reproduced.

4. In a color television image-reproducing system, the

combination including:

a cathode ray tube having a screen comprising a plurality of groups of vertically oriented color phosphor strips, the strips of each group being capable of emitting light of different colors when excited by an electron beam and one of the color phosphor strips of each group being of greater width than the other color phosphor strips of the group which have equal widths, and two sets of index strips aligned with said phosphor strips and capable respectively of producing two mutually distinguishable sets of index signals when excited by an electron beam, there being one of each set of index strips -for each group of color phosphor strips and the index strips being of equal widths corresponding substantially to said equal width color phosphor strips and equally spaced from one another;

means for separately deriving said two sets of index signals from said cathode ray tube screen, all of said index signals having the same polarity;

means for inverting the polarity of one set of index signals and combining it with said other set of index signals to produce an indexing Wave having little or no phase shift relative to said index strips;

means for modulating said indexing wave in phase in accordance with hue and in amplitude in accordance with saturationV by color representative signals to produce a color control wave; and

means responsive to said color control wave to vary said electron beam excitation of said cathode ray tube screen in accordance with the image colors to be reproduced.

5. In a color television image-reproducing system, the

combination including:

an image-reproducing-device having a screen comprising a plurality of groups of vertically oriented color strips and a plurality' of sets of index strips aligned with said color strips, the number of index strips in each of saidV sets bearing the same fractional relationship to the number of said groups of-color strips, and means to scan said screen in a series of vertically spaced horizontal lines to excite said strips for the emission of light of different colors from respective ones of said color strips and the production of a plurality of mutually distinguishable sets of index signals by respective ones of said index sets;

means for separately deriving said plurality of sets of index signals from said Vimage-reproducing device screen;

means for combining said plurality of sets of index signals in such manner as to produce an indexing wave having little or no phase shift relative to said index strips;

means utilizing said indexing wave to produce a color control wave; and

means responsive to said color control wave to control the excitation of said image-reproducing device screen in accordance with the image colors to be reproduced.

References Cited by the Examiner UNITED STATES PATENTS 2,945,087 7/1960 Graham et al. 178-5.r 3,041,392 6/1962 Keiper et al. l78-5.4 3,130,262 4/1964 Rudd 178-*54 3,154,715 11/1964 Jackson et al. 178--5.4

FOREIGN PATENTS 550,716 12/1957 Canada.

55 DAVID G. REDINBAUGH, Primary Examiner.

ROBERT SEGAL, Examiner.

I. A. OBRIEN, Assslant Examiner. 

1. IN A COLOR TELEVISION IMAGE-REPRODUCING SYSTEM, THE COMBINATION INCLUDING: A CATHODE RAY TUBE HAVING A SCREEN COMPRISING A PLURALITY OF GROUPS OF VERTICALLY ORIENTED EQUAL WIDTH COLOR PHOSPHOR STRIPS, THE STRIPS OF EACH GROUP BEING CAPABLE OF EMITTING LIGHT OF DIFFERENT COLORS WHEN EXCITED BY AN ELECTRON BEAM, AND TWO SETS OF INDEX STRIPS ALIGNED WITH SAID PHOSPHOR STRIPS AND CAPABLE RESPECTIVELY OF PRODUCING TWO MUTUALLY DISTINGUISHABLE SETS OF INDEX SIGNALS WHEN EXCITED BY AN ELECTRON BEAM, THERE BEING ONE OF EACH SET OF INDEX STRIPS FOR EACH GROUP OF COLOR PHOSPHOR STRIPS AND THE INDEX STRIPS BEING OF EQUAL WIDTHS CORRESPONDING SUBSTANTIALLY TO ONE-HALF THE WIDTH OF ONE OF SAID COLOR PHOSPHOR STRIPS AND EQUALLY SPACED FROM ONE ANOTHER; MEANS FOR SEPARATELY DERIVING SAID TWO SETS OF INDEX SIGNALS FROM SAID CATHODE RAY TUBE SCREEN, THE TWO SETS OF INDEX SIGNALS BEIGN OF OPPOSITE POLARITIES; MEANS FOR COMBINING SAID TWO SETS OF INDEX SIGNALS TO PRODUCE AN INDEXING WAVE HAVING LITTLE OR NO PHASE SHIFT RELATIVE TO SAID INDEX STRIPS; MEANS FOR MODULATING SAID INDEXING WAVE IN PHASE IN ACCORDANCE WITH HUE AND IN AMPLITUDE IN ACCORDANCE WITH SATURATION BY COLOR REPRESENTATIVE SIGNALS TO PRODUCE A COLOR CONTROL WAVE; AND MEANS RESPONSIVE TO SAID COLOR CONTROL WAVE TO VARY SAID ELECTRON BEAM EXCITATION OF SAID CATHODE RAY TUBE SCREEN IN ACCORDANCE WITH THE IMAGE COLORS TO BE REPRODUCED. 